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91.
Syeda?Humaira?TasnimEmail author Shohel?Mahmud Roydon?Andrew?Fraser 《Heat and Mass Transfer》2012,48(2):329-342
The effects of material, geometry, length and position of the porous channels on energy transfer in air-filled enclosures
carrying a compressible pulsating wave are investigated. The pulsating fluid motion is created by an acoustic driver in a
resonant chamber. Three different porous materials (Corning Celcor, Reticulated Vitreous Carbon (RVC), and Mylar plastic),
three different geometries (square, open foam, and circular cross-section), six different lengths, “L” (varying between 1 and 6.5 cm, L = 0.01–0.068 λ, where λ is the wavelength of the fundamental acoustic mode), and eight different positions (hot end of the
channel, varying between 0.5 and 8 cm) of the channels from the pressure anti-node is experimentally measured. The surface
temperature distribution on the channel wall and temperature difference generated across the channel walls are measured while
energy flow along the channel walls is calculated analytically. The experimental results are compared with a 1-D numerical
code and found excellent agreement. The material, geometry, length, and position of the porous channel strongly affect the
energy interactions between the porous channel and the working fluid. The temperature difference generated across the porous
RVC channel increases as the porosity increases form 20 to 80 PPI; but decreases if the porosity increases further. Corning
Celcor shows improved temperature difference generated across the channel as the length of the channel increases; but then
decreases if the length is further increased. The results of this study are applicable to the design of thermoacoustic devices. 相似文献
92.
Roger?I.?TannerEmail author Christopher?Ness Arif?Mahmud Shaocong?Dai Jiyoung?Moon 《Rheologica Acta》2018,57(10):635-643
The role of friction in non-colloidal suspensions is examined with a model which splits the viscosity into a frictionless component (τ*) plus a frictional component which depends on the ratio of the particle pressure (P) to the shear stress (τ). The model needs the input by computation of τ* and P and a suitable choice of particle friction coefficient (μ). It can be extended to elongational flows and cases where sphere roughness is important; volume fractions up to 0.5 are considered. It is shown that friction acts in a feedback or “bootstrap” manner to increase the suspension viscosity. The analysis is also useful for deducing the friction coefficient in suspensions from experimental data. It was applied to several sets of experimental data and reasonable correlations of the viscosities were demonstrated. An example of the correlation for spheres in a silicone oil is shown for volume fractions 0.1–0.5. 相似文献
93.
The present work deals with controlled mechanical systems subject to holonomic constraints. In particular, we focus on underactuated systems, defined as systems in which the number of degrees of freedom exceeds the number of inputs. The governing equations of motion can be written in the form of differential-algebraic equations (DAEs) with a mixed set of holonomic and control constraints. The rotationless formulation of multibody dynamics will be considered [1]. To this end, we apply a specific projection method to the DAEs in terms of redundant coordinates. A similar projection approach has been previously developed in the framework of generalized coordinates by Blajer & Kołodziejczyk [2]. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
94.
95.
Mahmud Abu-Odeh Dr. Katharina Bleher Neethinathan Johnee Britto Prof. Dr. Peter Comba Dr. Michael Gast Prof. Madhavan Jaccob Dr. Marion Kerscher Dr. Saskia Krieg Marius Kurth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(44):11377-11390
The nonheme iron(IV)-oxido complex trans-N3-[(L1)FeIV=O(Cl)]+, where L1 is a derivative of the tetradentate bispidine 2,4-di(pyridine-2-yl)-3,7-diazabicyclo[3.3.1]nonane-1-one, is known to have an S=1 electronic ground state and to be an extremely reactive oxidant for oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) processes. Here we show that, in spite of this ferryl oxidant having the “wrong” spin ground state, it is the most reactive nonheme iron model system known so far and of a similar order of reactivity as nonheme iron enzymes (C−H abstraction of cyclohexane, −90 °C (propionitrile), t1/2=3.5 sec). Discussed are spectroscopic and kinetic data, supported by a DFT-based theoretical analysis, which indicate that substrate oxidation is significantly faster than self-decay processes due to an intramolecular demethylation pathway and formation of an oxido-bridged diiron(III) intermediate. It is also shown that the iron(III)-chlorido-hydroxido/cyclohexyl radical intermediate, resulting from C−H abstraction, selectively produces chlorocyclohexane in a rebound process. However, the life-time of the intermediate is so long that other reaction channels (known as cage escape) become important, and much of the C−H abstraction therefore is unproductive. In bulk reactions at ambient temperature and at longer time scales, there is formation of significant amounts of oxidation product – selectively of chlorocyclohexane – and it is shown that this originates from oxidation of the oxido-bridged diiron(III) resting state. 相似文献
96.
M. Ravikanti W. Malalasekera M. Hossain T. Mahmud 《Flow, Turbulence and Combustion》2008,81(1-2):301-319
A methodology of extending laminar flamelet model in its adiabatic form to a non-adiabatic form which can account for radiative heat loss as well as its effect on NO x pollutant has been developed. Coupling of radiation submodel with flamelet model is based on the enthalpy defect concept. Pollutant NO x has been calculated from solution of its transport equation containing source term which is derived from flamelet calculations. Flamelet calculations adopted GRI 2.11 reaction mechanism which accounts for detailed carbon and NO x chemistry. Depending on consideration of variation in scalar dissipation within flamelet calculations, the non-adiabatic form has been further divided into non-adiabatic model with single (NADS) and multiple scalar dissipation rates (NADM). Bluff-body stabilized CH4/H2 flame has been chosen as the test case to assess the capability of non-adiabatic models. Turbulence closure has been achieved with a Reynolds stress transport model. Calculations have also been carried out with a modified k-ε model for evaluation of relative performance of the two turbulence closures. Performance of non-adiabatic flamelet models in regard to the overall structure of the flame is reasonably good and the agreement is similar to that of the adiabatic flamelet model thereby indicating weakly radiating nature of the flame. However, the NADM model results in minor but encouraging improvement in NO mass fraction predictions by reducing the extent of overprediction observed with the adiabatic model. In contrast, the NADS model results in overprediction over and above the adiabatic predictions thereby showing that, it is imperative to consider variation in scalar dissipation rate in flamelet calculations to capture the effect of radiation on NO. The results also show that employing the modified k-ε model instead of the Reynolds stress transport model for turbulence closure in NADM calculations results in considerable overprediction in centerline NO mass fractions. 相似文献
97.
Hamim Mahmud Rivy M R C Mahdy Nabila Masud Ziaur Rahman Jony Saikat Chandra Das 《理论物理通讯》2020,72(4):45502-105
Even for a 100 nm interparticle distance or a small change in particle shape,optical Fano-like plasmonic resonance mode usually vanishes completely.It would be remarkable if stable Fano-like resonance could somehow be achieved in distinctly shaped nanoparticles for more than 1μm interparticle distance,which corresponds to the far electromagnetic field region.If such far-field Fano-like plasmonic resonance can be achieved,controlling the reversal of the far-field binding force can be attained,like the currently reported reversals for near-field cases.In this work,we have proposed an optical set-up to achieve such a robust and stable Fano-like plasmonic resonance,and comparatively studied its remarkable impact on controlling the reversal of near-and far-field optical binding forces.In our proposed set-up,the distinctly shaped plasmonic tetramers are half immersed(i.e.air-benzene)in an inhomogeneous dielectric interface and illuminated by?circular?polarized light.We have demonstrated significant differences between near-and far-field optical binding forces along with the Lorentz force field,which partially depends on the object’s shape.A clear connection is shown between the far-field binding force and the resonant modes,along with a generic mechanism to achieve controllable Fano-like plasmonic resonance and the reversal of the optical binding force in both far-and near-field configurations. 相似文献
98.
Sharmin Akther Rupa Md. Rassel Moni Md. Abdul Majed Patwary Md. Mayez Mahmud Md. Aminul Haque Jamal Uddin S. M. Tareque Abedin 《Molecules (Basel, Switzerland)》2022,27(5)
Polytopic organic ligands with hydrazone moiety are at the forefront of new drug research among many others due to their unique and versatile functionality and ease of strategic ligand design. Quantum chemical calculations of these polyfunctional ligands can be carried out in silico to determine the thermodynamic parameters. In this study two new tritopic dihydrazide ligands, N’2, N’6-bis[(1E)-1-(thiophen-2-yl) ethylidene] pyridine-2,6-dicarbohydrazide (L1) and N’2, N’6-bis[(1E)-1-(1H-pyrrol-2-yl) ethylidene] pyridine-2,6-dicarbohydrazide (L2) were successfully prepared by the condensation reaction of pyridine-2,6-dicarboxylic hydrazide with 2-acetylthiophene and 2-acetylpyrrole. The FT-IR, 1H, and 13C NMR, as well as mass spectra of both L1 and L2, were recorded and analyzed. Quantum chemical calculations were performed at the DFT/B3LYP/cc-pvdz/6-311G+(d,p) level of theory to study the molecular geometry, vibrational frequencies, and thermodynamic properties including changes of ∆H, ∆S, and ∆G for both the ligands. The optimized vibrational frequency and (1H and 13C) NMR obtained by B3LYP/cc-pvdz/6-311G+(d,p) showed good agreement with experimental FT-IR and NMR data. Frontier molecular orbital (FMO) calculations were also conducted to find the HOMO, LUMO, and HOMO–LUMO gaps of the two synthesized compounds. To investigate the biological activities of the ligands, L1 and L2 were tested using in vitro bioassays against some Gram-negative and Gram-positive bacteria and fungus strains. In addition, molecular docking was used to study the molecular behavior of L1 and L2 against tyrosinase from Bacillus megaterium. The outcomes revealed that both L1 and L2 can suppress microbial growth of bacteria and fungi with variable potency. The antibacterial activity results demonstrated the compound L2 to be potentially effective against Bacillus megaterium with inhibition zones of 12 mm while the molecular docking study showed the binding energies for L1 and L2 to be −7.7 and −8.8 kcal mol−1, respectively, with tyrosinase from Bacillus megaterium. 相似文献
99.
Mahmud Khan K.A. Gschneidner Jr. V.K. Pecharsky 《Journal of magnetism and magnetic materials》2012,324(7):1381-1384
The magnetothermal properties of pseudo binary Ho1−xErxAl2 alloys have been investigated by heat capacity measurements. Two anomalies are observed in the heat capacity of HoAl2. A sharp peak at 20 K represents the first order spin reorientation transition, and a second order anomaly occurs in the vicinity of the ferromagnetic transition at 32 K. As Ho is partially replaced by Er in Ho1−xErxAl2 the sharpness of the first order heat capacity peak diminishes with increasing Er concentration, while the temperature of this transition remains practically unaffected. The second order ferromagnetic transition shifts to higher temperature region with increasing Er concentration. The observed behaviors are explained considering the geometry of 4f charge densities of Ho3+ and Er3+ and the easy magnetization directions of HoAl2 and ErAl2. 相似文献
100.
Ali RB Atangwho IJ Kaur N Abraika OS Ahmad M Mahmud R Asmawi MZ 《Molecules (Basel, Switzerland)》2012,17(5):4986-5002
An earlier anti-hyperglycemic study with serial crude extracts of Phaleria macrocarpa (PM) fruit indicated methanol extract (ME) as the most effective. In the present investigation, the methanol extract was further fractionated to obtain chloroform (CF), ethyl acetate (EAF), n-butanol (NBF) and aqueous (AF) fractions, which were tested for antidiabetic activity. The NBF reduced blood glucose (p < 0.05) 15 min after administration, in an intraperitoneal glucose tolerance test (IPGTT) similar to metformin. Moreover, it lowered blood glucose in diabetic rats by 66.67% (p < 0.05), similar to metformin (51.11%), glibenclamide (66.67%) and insulin (71.43%) after a 12-day treatment, hence considered to be the most active fraction. Further fractionation of NBF yielded sub-fractions I (SFI) and II (SFII), and only SFI lowered blood glucose (p < 0.05), in IPGTT similar to glibenclamide. The ME, NBF, and SFI correspondingly lowered plasma insulin (p < 0.05) and dose-dependently inhibited glucose transport across isolated rat jejunum implying an extra-pancreatic mechanism. Phytochemical screening showed the presence of flavonoids, terpenes and tannins, in ME, NBF and SFI, and LC-MS analyses revealed 9.52%, 33.30% and 22.50% mangiferin respectively. PM fruit possesses anti-hyperglycemic effect, exerted probably through extra-pancreatic action. Magniferin, contained therein may be responsible for this reported activity. 相似文献